The field of the invention pertains to retainers for punches, the punches being used in punch presses in the stamping industry to form and pierce various materials. Punch retainers enable the punches to be accurately positioned with respect to the complementary die and to be quickly and easily replaced without loss of the accurate punch position at set-up.
Punch retainers are disclosed in a number of patents and other literature. U.S. Pat. No. 2,364,733 discloses circular punch and die retainers having an oblique threaded locking pin wedging a punch or die in position. Earlier U.S. Pat. No. 1,621,811 discloses punch and die retainers with an oblique spring loaded ball chamber. The ball is urged into engagement with a depression in the punch or die to retain the punch or die within the retainer. The ball is disengaged by an instrument inserted through a small port in the retainer. In the former patent the punch and die each directly abut the press platens and in the latter the punch and die abut hardened steel backing plates set in sockets in the press platens.
U.S. Pat. No. 3,563,124 discloses punch and die retainers having uniquely formed plugs acting as backing plates within the retainer. The backing plug also includes a centering device for the plug punch and retainer. U.S. Pat. No. 3,589,226 illustrates a ball detent retainer with the punch abutting the press platen. The ball detent spring is uniquely formed to wedge in the oblique borehole for the ball and spring.
More recently issued U.S. Pat. No. 4,558,620 and U.S. Pat. No. 5,038,599 disclose punch retainers having hardened backing plates fully separating the retainer body from the press platen. Locating dowel pins locate the backing plate with respect to the press platen and additional dowel pins and holes in the retainer body locate the retainer body relative to the backing plate in the former. In the latter the backing plate is permanently affixed to the retainer body before passages in the retainer for the dowel pins and punch are ground to final accuracy.
The addition of various backing plate configurations in most of the disclosures above adds an element of inaccuracy to the lateral position of the punch. In addition, the additional backing plate adds substantial part manufacturing time and assembly time to the manufacture of the complete retainer.
The external shape of the retainer is of importance to the versatility of the retainer where multiple punches are used. Most of the retainers available are round, substantially triangular or pentagonal. A summary of retainer shapes commercially available are shown in the specification sheets for TRULOCK.TM. retainers from Lane Punch Corporation and FDS.TM. retainers from Dayton Progress Corporation. The shape of the retainers determines how close together multiple punches may be fastened to the press platen.
The invention disclosed below comprises further improvements to the punch retainers. As noted above modern punch retainers are equipped with backing plugs or plates for the punches. The backing plugs or plates are of hardened steel to protect the press platens or die set from wear and impact damage. The separate bodies of the retainers are of alloy steel to reduce the cost and time to form the various holes and are subsequently casehardened before the final grinding step.